Headlight reflectors are known in the prior art and in particular are described in the following patents FR-A-2 536 502, FR-A-2 536 503, FR-A-2 583 139, FR-A-2 597 575, FR-A-2 599 120, FR-A-2 599 121, FR-A-2 600 024, FR-A-2 602 306, FR-A-2 609 146, FR-A-2 609 148, FR-A-2 621 679, FR-A-2 634 003, all in the name of the present Applicant, and all sharing the common characteristic of the reflector itself forming filament images having positions on a projection screen which are well determined as a function of a particular desired photometric distribution, in particular relative to a cutoff that the type of beam under consideration is required to have.
It will be understood that in order to provide satisfactory results, such a reflector must co-operate with a light source whose geometry is sufficiently well determined.
When the light source is an incandescent filament, the light-emitting outline is closely correlated to the physical configuration of the filament, and said physical configuration is generally established in reproducible manner and with satisfactory accuracy from one lamp to another. Thus, FIG. 1a of the accompanying drawings is a series of isoluminence curves representing the light emission pattern of such a filament, which filament is generally in the form of a rectilinear cylinder.
However, certain types of lamp exist in which the light emission geometry does not have these qualities. This may arise in filament lamps where the shape or the position of the filament varies significantly from one lamp to another, e.g. for manufacturing reasons, or else where the geometrical shape of the filament is poorly defined, e.g. by being curved.
This may also occur in arc lamps which are valued because of their efficiency at generating light and which are now being developed for use in motor vehicle headlights. This type of lamp has a light emission pattern whose outline varies considerably, both from one lamp to another and within the same lamp depending on its state (while heating up or under steady conditions), and in addition the outline of the emission pattern of such a lamp is extremely diffuse which makes it very difficult to obtain a sharp cutoff using conventional means.
It will be understood that when its source is malformed in this way, a reflector of the type mentioned above will give rise to images of the source which are positioned in a more random manner, particularly relative to a cutoff. This results, in particular, in the risk of some of the images of the source spilling over significantly above the cutoff, consequently dazzling the drivers of oncoming vehicles, or else in the photometric distribution of the beam being unsatisfactory with respect to the minimum light intensities as laid down by the regulations.
In manner analogous to FIG. 1a, FIG. 1b of the accompanying drawings represents the light emission pattern of an arc established between two electrodes E1 and E2. This figure also shows a rectangle representing the "equivalent filament" occupying the ideal light-emitting zone. It can be seen that very intense light radiation is emitted by zones lying relatively far from the ideal rectangle, with such malformation giving rise to corresponding malformation of the images of the source after reflection by the reflector.
The present invention seeks to mitigate these drawbacks of the prior art and to provide a headlight capable of using a source whose geometry may be ill-defined in conjunction with a reflector of the type defined above but without the quality of the resulting light beam being significantly degraded.